Hello and thank you for your question. Do you have an example of the Imgur-URL you used?
You are not allowed to use these URLs on Imgur to use them as image. The reason is: they can be used for embedding, but not for output as an image alone.
From your first example, you should actually use this URL: https://i.imgur.com/Yf44FI8.jpeg – you can find it by right-clicking on the image in the imgur view and calling up the image URL there.
You can test why the URLs you are using do not work in the block editor, for example. Select the “Embed” block there and insert the URL you mentioned. You will then see an embedding of the image. However, the External Files in Media Library plugin ensures that the image files themselves can be used. So in the block editor via the image block.
